Two different ways scientists use the word "theory"

I was reading a chemistry book for my own knowledge, and read that there are two different ways scientists use the word "theory". I figured this
would be an interesting discussion to have.

The first usage of the word "theory" is an explanation to a verified hypothesis. This is different from a law, because a "law" is just a statement
of observed facts. Hence the theory of gravity is an explanation to why gravity works the way it does, but the law of gravity is a statement (in this
case, a mathematical statement) of the fact of objects attracting each other.

The second usage of the word "theory" is in the sense that it is a body of knowledge, comprised of laws, theories, facts, arguments and so forth.
The interesting thing about this usage is that it doesn't have to necessarily be an explanation of a proven hypothesis, just a bunch of knowledge
about some related things.

Anyway, that is what I read and it makes sense to me. Which theories of science do you suppose have which definition attached to them?

The second usage of the word theory is to represent a systematic body of knowledge, compounded of facts, laws, theories in the limited sense
described above [the first usage], deductive arguments, and so on.

Taken from General Chemistry by Linus Pauling, Third Edition

Don't know if that helps much.

I haven't formally studied evolution, so forgive me if this is wrong, but I think the theory of evolution is a theory of the second kind. There is
much evidence for it like spontaneous mutation, fossils, genetic theory, etc. There is much knowledge to suggest it, but scientists haven't actually
demonstrated in a lab one organism evolving into another organism by the mechanisms suggested by the evidence. The hypothesis is not verifiable
(unless scientists can run an experiment for thousands and thousands of years), though the theory of evolution consists of vast body of knowledge that
makes for a compelling argument.

At least I think so, because the theory of gravity seems different to me, as an explanation for a proven hypothesis. Maybe evolution has been proven
as a hypothesis, I haven't really studied biology yet, and what I learned in high school, I forgot.

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